Trophic quality of waters in the Lagoa dos Patos estuary (RS, Brazil): a comparison between the margins and the port channel located in Rio Grande city

Monica Wallner Kersanach


Abstract: Objective: This study aimed to evaluate the variations of physico-chemical parameters, phytonutrients and the Trophic State Index (TSI) in the waters on the margins and in the Rio Grande Channel and then compared to the shallow waters in the inlet called Saco da Mangueira, located in the south of the city. Methods: Surface and bottom water samples were collected in three sites in the channel (margin and center) and in two sites in the Saco da Mangueira in different hydrological conditions in 2011. Results: Waters in the Saco da Mangueira are very contaminated by phosphate and nitrogenous compounds. The TSI classifies these waters as being hypereutrophic, the consequence of both the release of effluents which were poorly treated and the low water flow in the inlet. Contamination was mild on the margins of the channel, where waters were classified as being eutrophic and mesotrophic. Trophic balance (mesotrophic waters - oligotrophic surface - bottom) was found in the center of the channel as a consequence of strong water flow and dilution of contaminants coming from the margins. Conclusion: Spatial variation in the TSI value enabled clear distinction to be observed between the areas on the margins and in the channel because it reflected the punctual presence of anthropogenic input in the marginal waters, mainly in the Saco da Mangueira. Effluent treatment must be required in order to control severe trophic imbalance in the waters on the margins of the city. Variations of the proposed index are a useful tool to identify sources of phosphate compounds in other aquatic environments.


effluents, organic contamination, phytonutrients, Trophic State Index

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